High-vacuum device



HIGH-VACUUM DEVICE Filed Feb. 2, 1953 8 Radio Tube 9-- Valve Mechanical Pump I8 26 lNVENToRs 650 w. CA FIG. 2 BY RIC DB.LA NCE ATTORNEY United States Patent @tifice l 2,714,484 HIGH-VACUUM DEVICE George W. Carr, Manchester, and Richard B. Lawrance,

Cambridge, Mass., assignors to National Research Corporation, Cambridge, Mass., a corporation of Massachusetts Application February 2, 1953, Serial No. 334,654 5 Claims. ((11.230-101) This invention relates to a high-vacuum device and more particularly to a combination of a high-vacuum diffusion pump and oil trap or separator.

A principal object of the invention is to provide a high-vacuum evacuating apparatus which can be opened to atmospheric pressure for short periods of time, while the pump is running, without losing appreciable quantities of pump oil.

Another object of the invention is to provide an oil trap or separator in the foreline of a diffusion pump to separate entrained oil droplets from the onrushing gases and to return the oil to the pump.

Still another object of the invention is to provide a high-vacuum evacuating apparatus which is particularly adapted for use on short pumping cycles such as the evacuation of radio tubes on automatic tube making and tube sealing equipment.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein there are shown diagrammatic sectional views of the preferred embodiments of the present invention.

Figure 1 is a diagrammatic sectional view of the oil separator and diffusion pump; and

Figure 2 is another diagrammatic sectional view taken along the line 2--2 of Fig. 1.

When diffusion pumps are opened to atmospheric pressure for short periods of time, while the pump is running, such as in the evacuation of radio tubes, the inrushing air is capable of entraining a considerable quantity of the diffusion pump oil and carrying it through the foreline and out of the pump. In such evacuating systems, much time and expense is encountered in replacing the large quantities of pump oil lost. In general, the present invention is directed to a combination of a high-vacuum diffusion pump and an oil trap or separator capable of centrifugally separating entrained oil droplets from high-velocity onrushing gases passing through the foreline during the initiation of the evacuation of a radio tube or the like and of returning the pump oil to the diffusion pump for further use. The oil trap or separator preferably comprises an upwardly extending conical chamber provided with a tangential inlet at the bottom for the passage of entering air and oil droplets from the foreline. A11 exit passage at the apex of the conical chamber provides for the escape of air to a mechanical pump. The bottom of .the conical chamber, the inlet and exit passages, are all inclined upwardly from the diffusion pump so that the separated oil can freely flow by gravity in an unobstructed path back to the diffusion pump.

Referring now to Fig. 1, the diffusion pump body is illustrated at 10. The diffusion pump is not entirely illustrated, but a pump such as that described in U. S. Patent 2,585,139 is one preferred type which may be employed with the present invention. This type of all valve is opened, air from the radio tube and ZJMAM Patented Aug. 2, 1955 diffusion pump is provided with a helical wire coil located between the pumping chamber and the boiler, and has been found to be quite effective in preventing substantial losses of oil due to pressure bursts within the boiler and jet tube assembly when a radio tube, for example, is being initially evacuated through the diffusion pump by the mechanical backing pump. At the time of such sudden inrush of high-pressure air, however, the pumping oil vapors which are in transit between the jet tube assembly and the pump casing are unavoidably en trained and carried out of the pump so that after long operating periods a substantial oil loss has been found to occur. The present invention provides for the entrapment of such oil mists and of returning the oil to the pump.

The pump is provided with a cooling coil 12 which is wrapped around the outside of the pump body 10. The foreline 14 is connected to the pump body adjacent an opening 16 in the pump body, this foreline extending preferably upwardly to an oil trap or separator 18.

The oil separator comprises a main body 20 which includes a lower cylindrical chamber 19 and an upper conical chamber 21. The bottom of the cylindrical chamber 19 is preferably closed by a plug 22 which is made vacuumtight by means of an O ring 24. This plug 22 is preferably made removable so as to facilitate cleaning of the. interior of the separator.

The foreline 14 is connected to the body of the separator so that the gases and vapors enter the cylinder chamber 19 in a tangential laminar flow. This is achieved by providing a tapered member 25 (Fig. 2) in the end of foreline 14 which directs the gases and vapors in a smooth converging path into an opening 26 which is tangential to chamber 19. For escape of oilfreed vapors from the separator, there is provided an opening 30 at the apex of the conical chamber 21. This opening is connected to an extension 32 of the foreline which, in turn, is connected to a suitable mechanical vacuum pump 34. As a result of this above construction of the separator 18;, the gases and entrained particles of oil spiral upwardly and inwardly as they travel through the separator. The high tangential velocity of the entering gases and the decreasing radius of the spiral subjects the oil particles to large centrifugal forces which deposit the oil particles in a thin film on the surfaces of the chambers 19 and 21. As seen best in Fig. 1, the opening 26 and the bottom of chamber 19 are arranged to extend upwardly from the diffusion pump it), so that the separated oil can flow freely back to the foreline 14 and thence to the pump 10.

In the evacuation of radio tubes, utilizing the present invention, a radio tube 3 is connected to the evacuating system by means of a valved connection 9. When this connecting parts rushes into the interior of the diffusion pump. While a diffusion pump of the type described in the above mentioned U. S. Patent 2,585,139 is particularly designed for, and is particularly effective in, preventing these bursts of air from blowing oil out of the boiler, it cannot prevent entrainment of oil vapors and dropiets in transit from the jets back to the boiler entrance. Thus, the entrainment of even minute quantities of oil per cycle can have a tremendous cumulative effect when it is considered that continuous operation of tube making machinery on a 24-hour a day basis will give approximately 1440 bursts of air through the pump per day. With the present invention, the initial burst of air deposits substantially all of its entrained oil in the separator 18, this deposited oil having ample time to drain back to the pump boiler be fore the next burst of air passes up the foreline 1 5. It is necessary that the viscosity of the returning oil be reasonably low at the attained temperature of the separator 18 and foreline 14 in order that the film of returning oil shall not be excessively thick and subject to drop detachment by the inrushing bursts of air. Too low a temperature can also cause partial or complete clogging of the passages 33 and 26. Hence, it is preferred that no substantial amount of cooling be provided on the separator. Thus the, oil in the separator is maintained relatively warm and fluid so that it can flow freely back to the pump. To achieve this purpose, the separator 18 is preferably made, as illustrated, of a fairly massive construction which has low heat loss. Additionally, the configuration of the lower portion of cooling coil 12 can be so designed as to produce the desired temperature range for the separator assembly 13, since the point of connection of the foreline 14 to the pump casing if? is intermediate between the hot boiler 13. and the cooling coil 12.

The oil separator of the present invention was tested under conditions similar to those encountered in the continuous automatic evacuation of radio tub-es. In the first test 26.5 cc. of pump oil was used in the ditfusion pump. The test was run continuously for 21 days with the diffusion pump opcning to atmospheric pressure at the rate of once a minute. At the end of 21 days, the amount of pump oil left in the pump was 19.6 cc. In a similar test under the same conditions, but which employed no oil separator 18, the initial charge of oil (24.75 cc.) was completely gone at the end of 12 continuous days of operation. As can be seen, the oil separator of the present invention greatly minimizes the problem of substantial oil losses during the short pumping cycles encountered in the evacuation of radio tubes.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawing, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for evacuating radio tubes and the like wherein the evacuating apparatus is periodically opened to atmospheric pressure as each new, unevacuated tube is connected thereto, the apparatus comprising an oil diffusion pump and means for preventing loss of oil in the form of mist due to bursts of air passing through the diffusion pump at high velocity, said means comprising a trap for centrifugally separating oil droplets from high velocity air passing through the forcline of the diffusion pump, said trap comprising means defining an upwardly extending chamber having a conical top means connected to the diffusion pump foreline providing a tangential inlet passage for air and oil droplets entering the bottom of said chamber from the foreliue, and means providing an exit passage at the apex of the conical chamber top for escape of the air to a mechanical pump, the bottom of the chamber, the inlet and exit passages being all inclined upwardly as seen from the diffusion pump so that the pumped air passes upwardly from the diffusion pump and the separated oil can flow by gravity in an unobstructed path back to the diffusion pump.

2. Apparatus for evacuating radio tubes and the like wherein the evacuating apparatus is periodically opened to atmospheric pressure as each. new unevacuated tube is connected thereto, the apparatus comprising an oil diifusion pump and means for preventing loss of oil in the form of mist due to bursts of air passing through the diffusion pump at high velocity, said means comprising a trap for centrifugally separating oil droplets from high velocity air passing through the foreline of the diffusion pump, said trap comprising means defining a conical chamber, means connected to the diffusion pump foreline providing a tangential inlet passage for air and oil droplets entering said chamber from the foreline, means providing an exit passage for the escape of air to a mechanical pump, the conical chamber being arranged so that the separated oil can flow by gravity back to the diffusion pump.

3. Apparatus for evacuating radio tubes and the like wherein the evacuating apparatus is periodically opened to atmospheric pressure as each new, unevacuated tube is connected thereto, the apparatus comprising an oil diffusion pump and means for preventing loss of oil in the form of mist due to bursts of air passing through the diffusion pump at high velocity, said means comprising a trap for centrifugally separating oil droplets from high velocity air passing through the foreline of the difiusion pump, said trap comprising means defining an upwardly extending chamber having a conical top, means connected to the diffusion pump foreline providing a tangential inlet passage for air and oil droplets entering the bottom of said chamber from the foreline, a removable plug serving as a bottom for said chamber and providing access to said chamber, an O ring providing a vacuumtight seal for said plug, and means providing an exit passage at the apex of the conical chamber top for escape of the air to a mechanical pump, the bottom of the chamher, the inlet and exit passages being all inclined upwardly as seen from the diffusion pump so that the pumped air passes upwardly from the diffusion pump and the separated oil can flow by gravity in an unobstructed path back to the diffusion pump.

4. Apparatus for evacuating radio tubes and the like wherein the evacuating apparatus is periodically opened to atmospheric pressure as each new unevacuated tube is connected thereto, the apparatus comprising an oil diffusion pump and means for preventing loss of oil in the form of mist due to bursts of air passing through the diffusion pump at high velocity, said means comprising a trap for centrifugally separating oil droplets from high velocity air passing through the foreline of the diffusion pump, said trap comprising means defining an upwardly extending chamber having a conical top, means connected to the diffusion pump foreline providing a tangential inlet passage for air and oil droplets entering the bottom of said chamber from the foreline, means adjacent to said tangential inlet passage for providing smooth laminar flow of air and oil from said foreline into said chamber, and means providing an exit passage at the apex of the conical chamber top for escape of the air to a mechanical pump, the bottom of the chamber, the inlet and exit passages being all inclined upwardly as seen from the diffusion pump so that the pumped air passes upwardly from the diffusion pump and the separated oil can flow by gravity in an unobstructed path back to the diffusion pump.

5. Apparatus for evacuating radio tubes and the like wherein the evacuating apparatus is periodically opened to atmospheric pressure as each new unevacuated tube is connected thereto, the apparatus comprising an oil diffusion pump and means for preventing loss of oil in the form of mist due to bursts of air passing through the diffusion pump at high velocity, said means comprising a trap for centrifugally separating oil droplets from high velocity air passing through the foreline of the diffusion pump, said trap comprising means defining a conical chamber, means connected to the diffusion pump foreline providing a tangential inlet passage for air and oil droplets entering said chamber from the foreline, means providing an exit passage for the escape of air to a mechanical pump, said means defining the conical chamber being arranged to provide only slight cooling to the separated oil so as to maintain the oil relatively warm and fluid and thus facilitate its return to the diffusion pump, the conical chamber being arranged so that the separated oil can flow by gravity back to the dilfusion pump.

References Cited in the file of this patent UNITED STATES PATENTS Lawrence et a1 Feb. 12, 1952 

